Blue tit behaviour question

Morning all Have a couple of questions on some blue tit behaviour I've been seeing. I put my first nest box up back in late March and within (literally) 45 minutes two blue tits were checking it out and took up residency! I am super chuffed and have been tracking their progress since. They now have chicks in there which hatched about 7 days ago. I feed all the birds wax worms and meal worms every morning and the two blue tits are always first up - they even fly onto the feeders while I'm still holding them and have become very relaxed around me (though not other people, which is good). Initially both male and female were equally feeding the chicks - in and out a dizzying amount of times a day. But in the last couple of days I've noticed that the female takes a worm, goes inside, and then stays inside for a while. This behaviour most irritates the male who sits outside with a worm in his beak waiting and squawking for her to come out... flying up to the hole in an agitated fashion and then away again, almost like he's trying to coax her back out. Sometimes he succeeds and she flies out and then he goes straight in and out again for more food, or sometimes he gives up and goes in there with her still inside and then flies out again to get more food. I wondered why the female might be reluctant to come out - is it typical behaviour that the female wants to stay with the chicks inside? Whatever it is it seems to most annoy the male who is doing a sterling job of feeding them! I also noticed that when I first put out the worms in the morning that the female is still doing the courtship feeding thing of flapping her wings and squeaking like she wants to be fed. Is it typical for this to go on even when they are at the stage where chicks have hatched? (The male completely ignores her and so she gives up and starts feeding the chicks). Is my female blue tit just particularly high maintenance?! :)